In many applications, such as in the field of firefighting on board ships, there is a need for a portable pump which is compact and light in weight and which can produce a high lift while maintaining a steady high flow volume. It is the general object of the invention to provide a portable engine-pump assembly that achieves this result.
To this end, there is provided in accordance with the invention an engine-pump assembly comprising a high speed, lightweight engine of the two-cycle type used in outboard engines and a lightweight pump using a double-suction impeller capable of producing a high lift while maintaining a steady high flow volume. The engine is arranged with a vertical crankshaft coupled to a vertical pump shaft for driving the same. The high efficiency achieved by the engine-pump assembly of the invention is derived partly from the double suction arrangement thereby providing good ratio between the impeller eye or inlet diameter and the outer diameter of the high speed pump impeller. When using high speed engines of the indicated type, it is desirable to keep the impeller diameter to a minimum so as to keep the horsepower required to a minimum. The use of a typical centrifugal pump for the relatively high volume and high lift conditions required presents a problem in that there would be a relatively large impeller inlet diameter compared to the impeller outer diameter and consequently a very short passage through the impeller to control the flow of water resulting in an inefficient pumping action. By the use of a double-suction pump impeller in accordance with the invention it is possible to reduce the impeller diameter and still achieve a good ratio between the impeller inlet and outlet and to provide sufficient passage space for controlling the flow of water through the impeller. While double-suction pumps are known, they are usually used on industrial pumps with horizontal shafts where the flow is in a straight horizontal line between the suction and discharge of the pump. It is not obvious to use a double-suction pump with a vertical pump shaft where the inlet and outlet are in line as in the configuration of the invention to be described more fully hereafter. The double-suction pump in accordance with the invention is designed to achieve maximum efficiency on the impeller so that the pump provides good vacuum capacity or high lift capacity so that there will be a good flow volume even with the high suction lift required for shipboard use.
Another feature of the invention is the design of the assembly so that hydraulic thrust loads are practically eliminated on the pump shaft whereby the bearings of a standard commercial outboard engine are sufficient to sustain the additional load of the pump impeller. To this end, the pump is not only a double-suction impeller pump but it is also a double-discharge volute design having two cutoffs which are spaced 180.degree. apart so as to take the radial hydraulic thrust load off the pump shaft. The design is such that any hydraulic radial thrust load built up in one volute of the pump is counterbalanced by equal thrust load on the opposite volute. Thus, with the double-suction impeller you cannot have any axial thrust load and with the double cutoff you eliminate the radial thrust load. In a centrifugal pump, the discharge cutoff is the point on the discharge body where the scroll starts for collecting the water that comes off the impeller. This pump structure actually cuts the water off the impeller and for that reason it is referred to as a "cutoff". It is noted that by eliminating all the thrust load on the pump shaft, the assembly is able to use the bearings on the engine to support the entire thrust load of the assembly.
Another feature of the invention is the novel drive coupling between the engine crankshaft and the pump impeller shaft. Briefly stated, this is achieved by the provision of an internal spline on an extension of the engine crankshaft. The pump body is then mounted on the engine body accurately by the use of piloting in a manner such that the pump impeller shaft is maintained to be concentric with the engine crankshaft, the impeller shaft being provided with an external spline which mates telescopically with the internal spline of the engine crankshaft. A unique feature of the alignment is the utilization of a bore in the engine crankcase housings for the crankshaft bearing to pilot this upper half of the pump body. Various alignment means are utilized so that the pump impeller shaft lines up accurately with the engine crankshaft so that these shafts run true and there are no thrust loads imposed upon the engine bearing by reason of the drive coupling. Accordingly, the assembly only needs to contain the thrust forces of the engine itself.
Another feature of the invention is the provision of a novel priming means for the pump. To this end, there is provided a plug means for a priming port that goes directly into the inlet passage at the highest point thereof and a primer bowl for delivering water thereto during priming.
Another feature of the invention is the provision of a novel discharge valve. The construction is such that the upper half of the pump body acts as a cover for a ball valve and the bottom half of the pump body acts as the main body of the valve. The ball valve member is dropped into place while the upper and lower halves of the pump body are separated, it being important that the pump body halves provide bearing supports that are in perfect alignment to receive the ball valve stems. Another feature of the ball valve is the arrangement providing for preloading of the ball against an O-ring seal which serves as the valve seat for the valve. The O-ring seal is provided with a steel insert and is received in a discharge fitting, which anchors to the lower housing. The O-ring seal is preloaded against the ball valve member by means of a preselected number of shims or gaskets positioned between the discharge fitting and the lower body of the pump.
Another feature of the invention is the construction of the pump body such that it achieves a plurality of functions. In accordance with the invention the lower half of the pump body contains the inlet and outlet as well as the discharge valve all in one casting with main passages being open at the top and sides. Also, the body has both the discharge and the volute as well as the double cutoff to retain radial balance on the impeller so as not to load the engine as described above. The upper half of the pump body is designed to form a one-piece mounting on the face of the engine which, in effect, becomes the mounting head for the assembly. The two pump halves are split in such a way as to give access to the critical volute passages so they may be manufactured with smooth surfaces for maximum efficiency.
Another feature of the invention is the design whereby any leakage from the seal located between the pump shaft and the pump housing is such that the leakage is open to atmosphere all around the pump shaft so that any weepage of water through the seal will not migrate up into the engine but is free to enter the atmosphere.
Another feature of the invention is the various design features which produce a very compact assembly. To this end, the engine exhaust is arranged to run directly through the upper half of the pump body and means are provided to attach a fitting to the upper half of the pump body to run the exhaust gases to a muffler. Also serving to achieve a compact structure is the arrangement whereby a plurality of functions are combined in a single element, such as the design whereby the upper half of the pump body also becomes the pump head which is normally an additional piece in a typical design. By way of example, an engine pump assembly in accordance with the invention has been designed to produce 55 horsepower in a package that is 24 by 21 inches in size and 24 inches in height.
Another feature of the invention is the provision of means for injecting water into the hot exhaust gases to cool them so they can be carried away with a rubber hose at a temperature that will not destroy the hose. To this end, a combination check valve, exhaust muffler, water trap and hose coupling is provided. The design is such that any water that would condense out in the exhaust system is kept from getting back into the engine. To this end, there is provided a ball check valve which floats in water in a water trap inside the muffler and allows the water to drain out to the atmosphere.
Another feature of the invention is the construction of light weight discharge and suction caps which are made from stampings in such a way that they provide spring clips whereby the caps can be taken off very rapidly and are held in place by the threads on the external surface of the suction and discharge pipes.